1. Field of the Invention
This invention relates to radio receivers and in particular, though not exclusively, it relates to radiotelephone receivers operable with different types of multiple access networks.
2. Description of the Related Art
Reference is made to the paper on xe2x80x9cRecent Advances in RF Integrated Circuitsxe2x80x9d by Behzad Razavi published in IEEE Communications Magazine December 1997 for a description of the prior art and technological background relating to transmitter/receiver architectures.
The following abbreviations and terms are used herein:
GSM: Global System for Mobile communications, (formerly Groupe Special Mobile)
W-CDMA: Wide band code division multiple access
TDMA: Time division multiple access
FDD: Frequency division duplex
UMTS: Universal mobile telecommunications system
FDMA: Frequency division multiple access
DUAL MODE: A receiver designed to operate with two networks, each network having a different type of multiple access.
MULTI-MODE: A receiver designed to operate with more than two networks each network having a different type of multiple access.
RF: Radio frequency
IF: Intermediate frequency
A TDMA system such as GSM has its allocated bandwidth divided into channels, 200 kHz for GSM, with users sharing time within each channel by the allocation of a time slot. The receiver for this TDMA system must therefore select a 200 kHz channel. For W-CDMA, However, the whole of the allocated bandwidth is received and multiple access is provided by code division. One such W-CDMA system is UMTS.
It is convenient for a single transceiver to be capable of operation with both TDMA and W-CDMA systems. In order to achieve such dual mode operation two separate receivers could be installed within the same telephone housing. A dual mode receiver such as will be described is not limited to the TDMA and W-CDMA modes and may for example be configured for reception of FDMA arid TDMA or FDMA and W-CDMA.
A dual mode receiver in which some stages of the receiver can be used for reception in e.g. both TDMA and W-CDMA modes would provide a significant reduction in the number and cost of components and in the volume of the receiver part of the phone. If the need for the SAW(Surface Acoustic Wave) filters commonly used at IF can be avoided implementation of the receiver will be greatly simplified.
It is an object of the present invention to provide a multi-mode receiver having some receiver stages common to all modes of reception and providing also good performance in both operating modes. A further object of the invention is to remove the need for SAW filters at IF so as to allow implementation of the receiver as an ASIC (Application Specific Integrated Circuit).
According to one aspect of the invention there is provided a dual mode radio receiver having a selectable first downconverter stage for each mode to convert RF to IF, a second downconverter stage to convert IF to baseband frequencies, said second downconverter stage being common to both modes, and channel selection at baseband frequencies by means of re-configurable filtering.
The invention may be extended to provide a multi-mode receiver wherein reception may be selected from more than two multiple access modes.
According to a second aspect of the invention there is provided a multi-mode radio receiver having a selectable first downconverter stage for each mode to convert RF to IF, a second downconverter stage to convert IF to baseband frequencies, said second downconverter stage being common to all modes, and channel selection at baseband frequencies by means of re-configurable filtering.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.